This invention is directed to an antenna for use in radar systems, and particularly to an array fed reflector antenna with multiple elevation beams.
There exist, a number of different types of antennas for use in radar systems. One type of antenna for use in radar systems is a multiple elevation beam reflector antenna which employs a vertically centered feed system, such as the model TPS-43 antenna manufactured by Westinghouse Electric Company. This antenna employs multiple feed horns which feed a reflector, and has the advantage of low cost. However, since a vertically centered feed system is employed, the antenna produces a large amount of blockage of the reflected beams, which is caused by this centered feed arrangement. Further, this type of reflector is only capable of horizontal polarization and has an azimuth sidelobe specification of 25 dB.
Another type of antenna system is the model TPS-70 antenna manufactured by Westinghouse Electric Company. This antenna is a planar array antenna with a matrix beamformer which uses edge slotted waveguide elements and achieves ultra-low sidelobes in azimuth. While the performance of the model TPS-70 is much better than the TPS-43, the cost of the TPS-70 is much greater than the TPS-43. Furthermore the model TPS-70 has certain disadvantages in that it squints and only radiates one polarization.
While the existing antennas of the type described above work well for their intended purpose, in fact the best performance for an existing reflector antenna only achieves 25 to 28 dB sidelobes. Thus, there is a need in the art for an antenna which provides the improved performance of a planar array antenna (such as the model TPS-70) while at the same time having a relatively low cost (such as the model TPS-43). Further, there is a need in the art for an antenna which achieves a planar wave front and produces three-dimensional detection, so that the angle of the target with respect to the horizon can be determined.
In prior art multiple elevation beam antennas, there exist devices which allow azimuth rows of electromagnetic energy radiating elements to be shared when several transmit elevation beams are to be formed. Available devices for allowing the sharing of such azimuth rows typically have taken the form of a switch which alternately actuates a low transmit beamformer and a high transmit beamformer. When the high transmit beamformer is actuated, the high transmit beamformer will drive both a set of high transmit azimuth rows and a set of shared transmit azimuth rows. When the low transmit beamformer is switched on, the low transmit beamformer will actuate both a set of low transmit azimuth rows and the set of shared transmit azimuth rows. This approach has inherent problems due to the reliability, power handling, and speed of the switches. Further, the combination of switches and networks required in this type of system tends to be very complex and costly. Thus, there is a need in the art for a simple and inexpensive means of providing a switching function, so that a set of shared transmit azimuth rows can be alternately actuated for two transmit elevation beams.